Whisk together flour, sugar, baking powder, baking soda, and salt in a large bowl. In another bowl, whisk together buttermilk, milk, eggs, and butter. Make a well in center of flour mixture, pour in milk mixture, and stir with a fork or whisk until well combined but still a bit lumpy. Fold in blueberries.
Heat a griddle (or large cast-iron or nonstick skillet) over medium and brush with butter. Working in batches, add 1/3 cup batter for each pancake. Cook until bubbles appear on surface and undersides are golden brown, about 2 minutes. Flip and continue cooking until other sides are golden brown, 1 to 2 minutes more. Transfer to a plate. Brush griddle with more butter between batches.
Serve, topped with butter and syrup, with sausages on the side.